Selecting manager names for 20 levels

Question

Hi,
Could you please help me on the following scenario?
Table "Base" holds the list of employee ids and names. Table "Mgr" holds the list of employee ids and their mgr ids (Who are also an employee) from level 1 to level 20. The requirement is to select the employee name with the 20 level mgr names (which can be obtained by referring the Base table).
For sample scenario, the following Creation Scripts add data for only 2 levels:
create table BASE
ENAME VARCHAR2(10),
EID NUMBER
insert into BASE (ENAME, EID)
values ('A', 1);
insert into BASE (ENAME, EID)
values ('B', 2);
insert into BASE (ENAME, EID)
values ('C', 3);
insert into BASE (ENAME, EID)
values ('D', 4);
insert into BASE (ENAME, EID)
values ('E', 5);
commit;
create table MGR
EID NUMBER,
MGRLVL1 NUMBER,
MGRLVL2 NUMBER
insert into MGR (EID, MGRLVL1, MGRLVL2)
values (1, 3, 4);
insert into MGR (EID, MGRLVL1, MGRLVL2)
values (2, 1, 5);
insert into MGR (EID, MGRLVL1, MGRLVL2)
values (3, 4, 2);
commit;
I tried to achieve the result using the following query:
select
m.eid,b1.ENAME,b2.ENAME lvlonemgrname ,b3.ENAME lvltwomgrname
from
base b1,
mgr m,
base b2,
base b3
where
b1.eid=m.eid
and b2.eid=m.mgrlvl1
and b3.eid=m.mgrlvl2
EID     ENAME     LVLONEMGRNAME     LVLTWOMGRNAME
1     A     C     D
2     B     A     E
3     C     D     B
It provided the output fine. But i used 2 "Base" table instances to populate 2 level manager names. In the actual requirement of selecting 20 manager names it makes me to add 20 instances of "Base" table.
With out creating 20 instances, we can use PL/SQL function and achieve the output.
Is there any other way to do this using SQL ? Please advise me

Answer 1

select m.eid, b1.ENAME,
       max(decode(b2.eid, m.mgrlvl1, b2.ENAME)) lvlonemgrname,
       max(decode(b2.eid, m.mgrlvl2, b2.ENAME)) lvltwomgrname
from base b1, mgr m, base b2
where b1.eid=m.eid
  and b2.eid in (m.mgrlvl1, m.mgrlvl2)
group by m.eid, b1.ENAME